Some(...) is just constructor for an option type as seen in other languages e.g. java's Optional, haskell's Maybe, c++'s std::optional. I assume that it's needed here because the field can't start as a null pointer otherwise. Maybe the vulnerability still works if the field starts with one string value and swaps to a different string value, but having it start holding None made for a simpler demo.

q.0 is the first field of q, which is anonymous. They could have just as well called it x and written q.x.